Guide

AutoCAD DGN : A file format for interoperability with MicroStation software

Introduction

If you work with CAD files from different platforms, understanding the DGN format is essential. This guide explains what DGN is, why and when to use it with AutoCAD, practical step-by-step methods to import, convert and edit DGN files, common errors and fixes, and alternative workflows. It is written for beginners but includes professional tips to improve interoperability and productivity.

What is DGN?

DGN is a CAD file format primarily used by Bentley Systems MicroStation. It stores vector geometry, annotations, levels (similar to layers), cell definitions (similar to blocks), and other CAD data. In multidisciplinary projects (infrastructure, civil engineering, architecture), DGN files frequently circulate between teams using MicroStation and teams using AutoCAD or AutoCAD-based products.

Purpose and Use Cases for DGN in AutoCAD

  • Interoperability: Share drawings between teams using MicroStation and teams using AutoCAD without losing critical geometry or metadata.
  • Infrastructure and civil projects: Civil engineers, transportation and utilities projects often use DGN as a standard.
  • Legacy data: Many organizations still archive designs in DGN; working with these files avoids costly redrawing.
  • Multidisciplinary coordination: Combine DGN data with DWG-based models in coordination and clash detection workflows.

Common use cases:

  • Importing a municipal base plan provided as DGN into an AutoCAD project.
  • Converting DGN deliverables to DWG for contractor use.
  • Attaching a DGN underlay for reference during redesign.
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Key Differences: DGN vs DWG

  • File owners: DGN — MicroStation; DWG — AutoCAD.
  • terminology: DGN uses levels, cells, references (similar to XREFs). DWG uses layers, blocks, xrefs.
  • Data fidelity: Some element types, fonts, or custom objects may translate imperfectly.
  • Metadata & attributes: Levels and attributes may not map 1:1; mapping strategies are often required.

Why, How and When to Use DGN with AutoCAD

When to use:

  • You receive geometry or documentation in .dgn and must integrate it into a DWG project.
  • You need to export AutoCAD data to DGN for a MicroStation-based client.
  • You must coordinate with agencies that mandate DGN deliverables.

Why use it:

  • To maintain project continuity and avoid redrawing.
  • To preserve as much original information as possible (alignment, levels, text).

How to approach it:

  1. Assess the DGN file: Check version (V7 vs V8), units, Coordinate system, and whether it contains raster references or external references.
  2. Choose an import/conversion method depending on your AutoCAD product and version.
  3. Map levels to layers, fonts and line styles, and clean the file after import.

How to Import DGN into AutoCAD — Step-by-Step

Note: Available commands depend on your AutoCAD product and version (AutoCAD, Civil 3D, Map 3D). If a command below is not available, use one of the alternative methods in the next section.

  1. backup files:

    • Always copy the original .dgn file before starting.

  2. Open AutoCAD (or AutoCAD Map 3D / Civil 3D).

  3. Import using the preferred tool:

    • Basic AutoCAD: Use the IMPORT command and select the .dgn file (or use the Import option from the Insert menu).
    • AutoCAD Map 3D: Use MAPIMPORT for more control over layers/feature mapping.
    • Civil 3D: Use DGNIMPORT if available, or IMPORT/Attach method.

  4. Configure import options:

    • Set units (meters/feet).
    • Choose whether to convert levels to layers or keep as reference properties.
    • Decide how to handle text and fonts (SHX mapping, TrueType substitution).

  5. Review the import:

    • Check layers (levels), text styles, blocks/cells, and geometry scale/position.
    • Run AUDIT to detect errors.
    • Use OVERKILL to remove duplicate geometry if needed.

  6. Fix and finalize:

    • Remap levels to your layer naming convention.
    • Replace unavailable fonts with local SHX or TTF fonts.
    • Purge unused items with PURGE.
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How to Export or Save DWG to DGN

Methods vary by product:

  1. Use a built-in export (if available):

    • Some versions of AutoCAD or the TrueView/Map tools allow Export > DGN or save as DGN.

  2. Use Bentley / third-party conversion:

    • Open DWG in MicroStation and use MicroStation’s export to DGN for high fidelity.
    • Use tools like Safe Software FME, Bentley translators, or ODA/Teigha converters.

  3. Recommendations:

    • Before export, standardize layers, fonts, and block names.
    • Check units and Coordinate systems.
    • Test with a small area first to validate mapping.

How and When to Edit DGN Content in AutoCAD

After importing, DGN content typically becomes editable DWG entities, but behavior depends on import method:

  • If elements converted to native AutoCAD objects: Edit using standard commands (MOVE, TRIM, PROPERTIES, EXPLODE, etc.).
  • If elements are attached as underlay/reference:
    • Use XCLIP/clip options or convert the underlay by importing or using a convert command.
  • If certain objects remain as proxy or non-native entities:
    • Use EXPLODE or conversion utilities, or re-import with different options.
    • For text or cells that didn’t translate, re-create as AutoCAD MText or Blocks.

When to avoid editing in AutoCAD:

  • If the DGN will be returned to MicroStation and must preserve MicroStation-specific objects; instead, request a DWG export from MicroStation or coordinate editing through MicroStation.

Alternative Methods and Tools

  • Use MicroStation to export a DWG directly — best fidelity.
  • Use AutoCAD Map 3D for advanced feature mapping and GIS coordinate system handling.
  • Use third-party converters: Safe Software FME, ODA File Converter, Bentley utilities.
  • Use online conversion services for small files (verify security and confidentiality).
  • Request the sender to provide both DGN and DWG versions when possible.

Common Errors and How to Fix Them

  • Problem: Geometry is scaled incorrectly.

    • Fix: Check and set units and insertion scale before importing; verify coordinate systems.

  • Problem: Text appears as boxes or wrong fonts.

    • Fix: Map missing SHX fonts to local equivalents or convert text to TTF on the source side.

  • Problem: Levels didn’t become layers or naming is inconsistent.

    • Fix: Use layer/level mapping tools during import or manually remap using the Properties palette or a script.

  • Problem: Proxy or custom MicroStation elements not editable.

    • Fix: Re-import with different options, use MicroStation to convert elements to basic entities, or request simplified export.

  • Problem: File too large or slow performance after import.

    • Fix: Use OVERKILL, PURGE, AUDIT, and consider splitting the file or using XREFs.

  • Problem: Raster images or references missing.

    • Fix: Ensure referenced raster files are available and paths are correct; reattach rasters if necessary.
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Tips for Better Interoperability

  • Always create a backup of original DGN/DWG files.
  • Agree on units, coordinate system and layer/level naming conventions before exchanging files.
  • Ask the DGN sender to export as DGN V8 (if possible) for better compatibility.
  • Use layer/level mapping tables to automate conversions.
  • Keep a font map (.fmp) or SHX/TFF library accessible across teams.
  • Validate conversions on a small sample before processing large datasets.
  • Use XREFs or references rather than embedding everything into one file to maintain performance.

FAQ

What AutoCAD versions support DGN import/export?

Support varies by product and version. Basic AutoCAD often supports DGN import via the IMPORT command; AutoCAD Map 3D and Civil 3D provide more advanced import tools (e.g., MAPIMPORT, DGNIMPORT). For guaranteed fidelity, use MicroStation or dedicated conversion tools.

Will importing a DGN file preserve all layers, text, and block data?

Many elements translate, but not always perfectly. Levels generally convert to layers, and cells often convert to blocks, but fonts, line styles, and proprietary MicroStation objects may require manual mapping or adjustment.

How do I preserve coordinate systems and georeferencing?

Use AutoCAD Map 3D or request georeferenced exports from MicroStation. Always verify and set units and coordinate systems during import to avoid misplacement or scaling issues.

Can I edit a DGN directly in AutoCAD without converting?

You can attach a DGN as a reference/underlay in some AutoCAD versions, but to fully edit geometry you typically import or convert it to native AutoCAD entities.

What should I do if text becomes unreadable after import?

Check for missing SHX fonts and map them to available fonts or ask for TrueType (TTF) text from the DGN author. Recreate critical annotations as MText if needed.

Is it better to Convert DGN to DWG or have the sender export to DWG?

If possible, ask the sender (MicroStation user) to export to DWG using their software for higher fidelity. If not possible, convert on your side but test results carefully.

Are there automated tools to map levels to my layer naming standard?

Yes. AutoCAD Map 3D offers feature mapping during import. You can also create scripts, LISP routines, or use third-party tools to apply consistent layer mapping.

How can I minimize data loss during conversion?

  • Communicate standards (units, fonts, layers) ahead of time.
  • Use MicroStation for final export if available.
  • Test conversions on sample data and adjust import settings.
  • Keep original files to reference any lost information.

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